Hollow core golf ball having a hardness gradient

ABSTRACT

A golf ball including a hollow core formed from a spherical inner core shell layer including a stiff thermoplastic composition. The shell layer has an outer surface, an inner surface, and an inner diameter to define a hollow center. Ann outer core layer is disposed about the shell layer and includes a thermoset material. An inner cover layer is disposed about the outer core layer and includes an ionomeric material having a first hardness. An outer cover layer is disposed about the inner cover layer and includes a polyurethane having a second hardness different from the first. The hollow center has a diameter of 0.15 to 1.1 inches, the thermoplastic inner core shell layer has a hardness of 85 Shore C or greater, and the stiff thermoplastic composition has a melt volume flow rate of about 5.0 cm 3 /10 min or less at 230° C./2.16 kg.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 13/737,026, filed Jan. 9, 2013, the disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to golf balls with a core having ahollow center surrounded by one or more core layers and one or morecover layers. Any of the core or cover layers may have a ‘negative’ or‘positive’ hardness gradient, depending on the desired construction.More particularly, the golf ball includes a core having a hollow centersurrounded by a thermoplastic ‘shell layer’, a thermoplastic core layer,and, optionally, at least one thermoplastic or thermoset intermediatecore layer.

BACKGROUND OF THE INVENTION

In recent years, virtually all golf balls are of a solid construction,typically including with a solid core encased by a cover, both of whichcan have multiple layers, such as a dual core having a solid center andan outer core layer, or a multi-layer cover having an inner and outercover layer. Golf ball cores and/or centers are formed from a thermosetrubber composition with polybutadiene as the base rubber. The cores areusually heated and crosslinked to create a core having certainpre-determined characteristics, such as compression or hardness, whichresult in a golf ball having the properties for a particular group ofplayers, whether it be professionals, low-handicap players, ormid-to-high handicap golfers. From the perspective of a golf ballmanufacturer, it is desirable to have cores exhibiting a wide range ofproperties, such as resilience, durability, spin, and “feel,” becausethis enables the manufacturer to make and sell golf balls suited todiffering levels of ability.

There remains a need, however, for golf ball constructions that allowdiffering properties to be achieved. One such novel construction with nopast commercial success is a golf ball having a hollow core—meaning theinnermost portion of the core is hollow surrounded by a ‘shell layer’and one or more core and cover layers. While, in the past, manycommercially-available golf balls have been constructed with non-solidcenters, such as liquid centers, very few golf balls having hollowcenters have ever been constructed.

While the patent literature references, mostly in a cursory manner, ahollow core as a suitable general alternative construction, very few areactually directed to a hollow core golf ball. For example, U.S. Pat. No.6,315,683 is generally directed to an over-sized (greater than 1.70inches) hollow solid golf ball where the hollow core is contained in athermoset rubber layer and covered with a single ionomer cover. Morerecently, U.S. Pat. No. 8,262,508 generally describes a golf ball havinga hollow center, a mid-layer, an inner cover, and an outer cover. Thehollow center and mid-layer are both formed from a thermoset rubbercomposition, and a conventional ‘positive hardness gradient’ (layerhardness gets softer in the direction of the interior of the layer). Thehollow ‘space’ has a diameter of 0.08 to 0.5 inches and the core layerhas a low surface hardness of 25 to 55 Shore C. The golf ball is coveredby a harder ionomer outer cover and a softer ionomer inner cover.

The inventive golf ball, however, has a hollow core surrounded by athermoplastic ‘shell layer’, a thermoplastic outer core layer,optionally one or more additional thermoset or thermoplastic corelayers, and one or more cover layers. Combining the hollow coreconstruction with variations in the hardness gradients of the adjoiningthermoplastic and/or thermoset core layers solves many of the problemsassociated with previous attempts at hollow core constructions.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball having a hollow core.The golf ball includes a spherical inner core shell layer formed from athermoplastic composition. The shell layer has an outer surface, aninner surface, and an inner diameter to define the hollow center. Thegolf ball also includes an outer core layer disposed about the shelllayer, the outer core layer including a thermoplastic material which maybe the same or different from that of the shell layer. An optional innercover layer is disposed about the outer core layer. The inner coverincludes an ionomeric material. The golf ball has an outer cover layerdisposed about the optional inner cover layer or the outer core layer.The outer cover includes a polyurea or a polyurethane material and has ahardness less than the hardness of the inner cover layer. The hollowcenter has a diameter of about 0.15 to 1.1 inches, the shell layer has asurface hardness greater than an inner surface hardness by about 0 to 5Shore C to define a hardness gradient, and the thermoplastic outer corelayer has a second hardness gradient different from the hardnessgradient of the shell layer.

In one embodiment, the second hardness gradient is about 0 Shore C. Inan alternative embodiment, the second hardness gradient is a negativehardness gradient of about 1 to 10 Shore C. In yet another embodiment,the second hardness gradient is a positive hardness gradient of about 1to 10 Shore C. The golf ball has a first volume and the hollow centerhas a second volume that is about 2% to 30% of the first volume. Thespherical inner core shell layer has a coefficient of restitution lessthan about 0.700 when measured at an incoming velocity of 125 ft/s.Also, the outer core layer has a coefficient of restitution, measured atan incoming velocity of 125 ft/s, higher than the coefficient ofrestitution, measured at an incoming velocity of 125 ft/s, of the innercore shell layer by 10-50%.

The present invention is also directed to a golf ball including a hollowcore. The golf ball has a spherical inner core shell layer including athermoplastic material. The shell layer has an outer surface, an innersurface, and an inner diameter that define the hollow center. The golfball has an outer core layer including a thermoplastic material. Anintermediate core layer is disposed between the shell layer and theouter core layer, the intermediate layer including a thermoplasticmaterial that is the same or different from that of the shell or outercore layer. An optional inner cover layer is disposed about the outercore layer and includes an ionomeric material. The golf ball has anouter cover layer disposed about the inner cover layer or outer corepayer. The outer cover includes a polyurea or a polyurethane materialand has a hardness less than the hardness of the inner cover layer. Thehollow center has a diameter of about 0.15 to 1.1 inches. The shelllayer has a surface hardness greater than the inner surface hardness byabout 0 to 5 Shore C to define a hardness gradient, and at least one ofthe thermoplastic outer core layer or the thermoplastic intermediatelayer has a second hardness gradient different from the hardnessgradient of the shell layer.

In one embodiment, the second hardness gradient is about 0 Shore C. Inan alternative embodiment, the second hardness gradient is a negativehardness gradient of about 1 to 10 Shore C. In yet another embodiment,the second hardness gradient is a positive hardness gradient of about 1to 10 Shore C.

The present invention is further directed to a golf ball having a hollowcore. The golf ball has a spherical inner core shell layer including athermoplastic material. The shell layer has an outer surface, an innersurface, and an inner diameter to define the hollow center. The golfball also has an outer core layer including a thermoplastic material andan intermediate core layer disposed between the shell layer and theouter core layer. The intermediate core layer includes a thermosetrubber composition. An optional inner cover layer is disposed about theouter core layer and typically includes an ionomeric material. The golfball has an outer cover layer disposed about the inner cover layer orouter core layer. The outer cover includes a polyurea or a polyurethanematerial and has a hardness less than the hardness of the shell layer.The hollow center has a diameter of about 0.15 to 1.1 inches. The shelllayer has a surface hardness greater than the inner surface hardness byabout 0 to 5 Shore C to define a hardness gradient, and thethermoplastic outer core layer has a second hardness gradient.

In one embodiment, the second hardness gradient is about 0 Shore C. Inan alternative embodiment, the second hardness gradient is a negativehardness gradient of about 1 to 10 Shore C. In yet another embodiment,the second hardness gradient is a positive hardness gradient of about 1to 10 Shore C. The thermoset intermediate core layer has a surfacehardness less than an inner surface hardness to define a negativehardness gradient. Alternatively, the thermoset intermediate core layerhas a surface hardness greater than an inner surface hardness to definea positive hardness gradient. The present invention is also directed toa golf ball including a hollow core formed from a spherical inner coreshell layer including a stiff thermoplastic composition. The shell layerhas an outer surface, an inner surface, and an inner diameter to definea hollow center. An outer core layer is disposed about the shell layerand includes a thermoset material. An inner cover layer is disposedabout the outer core layer and includes an ionomeric material having afirst hardness. An outer cover layer is disposed about the inner coverlayer and includes a polyurethane having a second hardness differentfrom the first.

The hollow center has a diameter of 0.15 to 1.1 inches, thethermoplastic inner core shell layer has a hardness of 85 Shore C orgreater, and the stiff thermoplastic composition has a melt volume flowrate of about 5.0 cm³/10 min or less at 230° C./2.16 kg.

The stiff thermoplastic composition typically has a melt volume flowrate of about 3.0 cm³/10 min or less at 230° C./2.16 kg, more preferablyabout 1.0 cm³/10 min or less at 230° C./2.16 kg.

The stiff thermoplastic inner shell layer may be formed from twopre-molded half shells or, alternatively, may be formed by blow molding,rotationally molding, or by gas injection molding. Preferably, the stiffthermoplastic composition has a hardness of about 90 Shore C or greater,more preferably about 95 Shore C or greater.

The outer core layer may include a polybutadiene rubber and, in oneembodiment, has a hardness equal to or less than the shell layerhardness. The outer core layer may have a thickness of about 0.015inches to about 0.15 inches or, more preferably, about 0.025 inches toabout 0.115 inches.

In another embodiment, the golf ball includes an intermediate layerdisposed between the outer core layer and the inner cover layer. Theoptional intermediate layer may be formed from a thermoset orthermoplastic material. In one embodiment, the inner cover layerhardness is greater than the outer cover layer hardness. In analternative embodiment, the outer cover layer hardness is greater thanthe inner cover layer hardness.

In a preferred embodiment, the golf ball has a first volume and thehollow center has a second volume that is about 2% to 30% of the firstvolume. The spherical inner core shell layer may have a coefficient ofrestitution less than about 0.700 when measured at an incoming velocityof 125 ft/s. The outer core layer may have a coefficient of restitution,measured at an incoming velocity of 125 ft/s, higher than thecoefficient of restitution, measured at an incoming velocity of 125ft/s, of the inner core shell layer by 10-50%.

The present invention is further directed to a golf ball including ahollow core formed from a spherical inner core shell layer including astiff thermoplastic composition. The shell layer has an outer surface,an inner surface, and an inner diameter to define a hollow center. Anouter core layer is disposed about the shell layer and includes athermoplastic material. An inner cover layer is disposed about the outercore layer and includes an ionomeric material having a first hardness.An outer cover layer is disposed about the inner cover layer andincludes a polyurethane having a second hardness different from thefirst. The hollow center has a diameter of 0.15 to 1.1 inches, thethermoplastic inner core shell layer has a hardness of 85 Shore C orgreater, and the stiff thermoplastic composition has a melt volume flowrate of about 5.0 cm³/10 min or less at 230° C./2.16 kg.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a is a plot of Shore C hardness versus distance from thecenter of the hollow core for one embodiment of a thermoplastic(TP)/thermoplastic (TP) hollow core golf ball; and

FIG. 1 b is a is a plot of Shore C hardness versus distance from thecenter of the hollow core for a second embodiment of a thermoplastic(TP)/thermoplastic (TP) hollow core golf ball.

DETAILED DESCRIPTION OF THE INVENTION

The golf balls of the present invention may include multi-layer golfballs, such as one having a core and a cover surrounding the core, butare preferably formed from a core having a hollow core and at least oneouter core layer, an inner cover layer, and an outer cover layer. Any ofthe core or cover layers may include more than one layer. The coverlayer of the golf ball may be a single layer or formed of a plurality oflayers, such as an inner cover layer and an outer cover layer.

The hollow core is formed of a thermoplastic ‘shell layer’ that containsa spherical hollow portion in its interior. In a preferred embodiment,the golf ball includes the thermoplastic hollow core and at least twoouter core layers, where the shell layer is formed from a thermoplasticmaterial, an outer core layer is formed from a thermoplastic material,and an intermediate core layer, disposed between the shell layer and theouter core layer, is formed from a thermoset material. In an alternativepreferred embodiment, the golf ball includes the thermoplastic hollowcore and at least two outer core layers, where the shell layer is formedfrom a thermoplastic material, an outer core layer is formed from athermoplastic material, and an intermediate core layer, disposed betweenthe shell layer and the outer core layer, is formed from a thermoplasticmaterial.

The shell, outer core, or intermediate core layers may have either aconventional “hard-to-soft” hardness gradient (i.e., the outermostsurface/portion of the layer is harder than the innermostsurface/portion), known as a “positive hardness gradient,” or a“soft-to-hard” hardness gradient (i.e., a “negative” hardness gradient)as measured radially-inward from the outer surface or portion of eachcomponent towards the innermost portion (i.e., from the outersurface/portion towards the inner surface/portion of the shell and/orcore layers). As used herein, the terms “negative” and “positive,” withrespect to hardness gradient, refer to the result of subtracting thehardness value at the innermost portion of the component being measured(e.g., the inner surface of a core layer) from the hardness value at theouter surface of the component being measured (e.g., the outer surfaceof an outer core layer). For example, if the outer surface of a corelayer has a lower hardness value than at the inner surface, the hardnessgradient will be deemed a “negative” gradient (a smaller number−a largernumber=a negative number), although the magnitude may be disclosed inthe application as the absolute value of the subtraction result incombination with the designation ‘negative’).

The thermoplastic shell, intermediate core layers, and outer core layersof the invention may have ‘positive hardness gradients’ or ‘negativehardness gradients’, as described above. Alternatively, the TP layersmay have a ‘zero hardness gradient’, defined herein to include a 0 ShoreC hardness gradient ±2 Shore C. The TP layer ‘positive hardnessgradient’ or ‘negative hardness gradient’ may be from about 0 Shore C toabout 10 Shore C, more preferably about 2 Shore C to about 8 Shore C,and most preferably about 3 Shore C to about 5 Shore C.

The thermoset shell, intermediate core layers, and outer core layers ofthe invention may have ‘positive hardness gradients’ or ‘negativehardness gradients’, as described above. Alternatively, the TS layersmay have a ‘zero hardness gradient’, defined herein to include a 0 ShoreC hardness gradient ±2 Shore C. The TS layer ‘positive hardnessgradient’ or ‘negative hardness gradient’ may be from about 1 Shore C toabout 30 Shore C, preferably about 2 Shore C to about 27 Shore C, morepreferably about 5 Shore C to about 25 Shore C, and most preferablyabout 10 to 20 Shore C. Other suitable TS ‘positive hardness gradient’or ‘negative hardness gradient’ core layers can be found in U.S. Pat.Nos. 7,537,529 and 7,537,530, the disclosures of which are incorporatedherein, in their entirety, by reference thereto.

A variety of the above TS and TP hardness gradient layers are envisionedand both ‘positive hardness gradients’ and/or ‘negative hardnessgradients’ may be combined to form the hollow cores of the inventionhaving various layers of this nature.

The surface hardness of the shell or core layers is obtained from theaverage of a number of measurements taken from opposing hemispheres ofthe particular layer, taking care to avoid making measurements on theparting line or any surface defects, such as holes or protrusions.Hardness measurements are made pursuant to ASTM D-2240 “IndentationHardness of Rubber and Plastic by Means of a Durometer.” Because of thecurved surface of the hollow core or core layers, care must be taken toinsure that they are centered under the durometer indentor before asurface hardness reading is obtained. A calibrated, digital durometer,capable of reading to 0.1 hardness units is used for all hardnessmeasurements and is set to take hardness readings 1 second after themaximum reading is obtained. The digital durometer must be attached to,and its foot made parallel to, the base of an automatic stand, such thatthe weight on the durometer and attack rate conform to ASTM D-2240.

To prepare the hollow core for hardness and hardness gradientmeasurements, the core (shell layer or with one or two core layers) isgently pressed into a hemispherical holder having an internal diameterapproximately slightly smaller than the diameter of the core, such thatthe core is held in place in the hemispherical portion of the holderwhile concurrently leaving the geometric central plane of the coreexposed. The core is secured in the holder by friction, such that itwill not move during the cutting and grinding steps, but the friction isnot so excessive that distortion of the natural shape of the core wouldresult. The core is secured such that the parting line of the core isroughly parallel to the top of the holder. The diameter of the core ismeasured 90° to this orientation prior to securing. A measurement isalso made from the bottom of the holder to the top of the core toprovide a reference point for future calculations. A rough cut, madeslightly above the exposed geometric center of the core using a band sawor other appropriate cutting tool, making sure that the core does notmove in the holder during this step. The remainder of the core, still inthe holder, is secured to the base plate of a surface grinding machine.The exposed ‘rough’ core surface is ground to a smooth, flat surface,revealing the hollow center of the core, which can be verified bymeasuring the height of the bottom of the holder to the exposed surfaceof the core, making sure that exactly half of the original height of thecore, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with acenter square and carefully marked and the hardness is measured at thecenter mark. Hardness measurements at any distance from the center ofthe core may be measured by drawing a line radially outward from thecenter mark, and measuring and marking the distance from the center,typically in 1- or 2-mm increments. All hardness measurements performedon the plane passing through the hollow center are performed while thecore is still in the holder and without having disturbed itsorientation, such that the test surface is constantly parallel to thebottom of the holder. The hardness difference from any predeterminedlocation on the core is calculated as the average surface hardness minusthe hardness at the appropriate reference point.

One or more of the shell layer and/or core layers may be formed from acomposition including at least one thermoset base rubber, such as apolybutadiene rubber, cured with at least one peroxide and at least onereactive co-agent, which can be a metal salt of an unsaturatedcarboxylic acid, such as acrylic acid or methacrylic acid, anon-metallic coagent, or mixtures thereof. Preferably, a suitableantioxidant is included in the composition. An optional ‘soft and fastagent’ (sometimes called a cis-to-trans catalyst), such as anorganosulfur or metal-containing organosulfur or thiol compound, canalso be included in the core formulation. Other ingredients that areknown to those skilled in the art may be used, and are understood toinclude, but not be limited to, density-adjusting fillers, processaides, plasticizers, blowing or foaming agents, sulfur accelerators,and/or non-peroxide radical sources.

The base thermoset rubber, which can be blended with other rubbers andpolymers, typically includes a natural or synthetic rubber. A preferredbase rubber is 1,4-polybutadiene having a cis structure of at least 40%,preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include BUNA® CB22 and BUNA®CB23, CB1221, CB1220, CB24, and CB21, commercially-available fromLANXESS Corporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BRrubbers, commercially available from UBE Industries, Ltd. of Tokyo,Japan; KINEX® 7245, KINEX® 7265, and BUDENE 1207 and 1208, commerciallyavailable from Goodyear of Akron, Ohio; SE BR-1220; Europrene® NEOCIS®BR 40 and BR 60, commercially available from Polimeri Europa; and BR 01,BR 730, BR 735, BR 11, and BR 51, commercially available from JapanSynthetic Rubber Co., Ltd; PETROFLEX® BRNd-40; and KARBOCHEM® ND40,ND45, and ND60, commercially available from Karbochem.

From the Lanxess Corporation, most preferred are the Nd- andCo-catalyzed grades, but all of the following may be used.: BUNA CB 21;BUNA CB 22; BUNA CB 23; BUNA CB 24; BUNA CB 25; BUNA CB 29 MES; BUNA CBNd 40; BUNA CB Nd 40 H; BUNA CB Nd 60; BUNA CB 55 NF; BUNA CB 60; BUNACB 45 B; BUNA CB 55 B; BUNA CB 55 H; BUNA CB 55 L; BUNA CB 70 B; BUNA CB1220; BUNA CB 1221; BUNA CB 1203; BUNA CB 45. Additionally, numeroussuitable rubbers are available from JSR (Japan Synthetic Rubber), UBEPOLsold by Ube Industries Inc, Japan, BST sold by BST Elastomers, Thailand;IPCL sold by Indian Petrochemicals Ltd, India; NITSU sold by Karbochemor Karbochem Ltd of South Africa; PETROFLEX of Brazil; LG of Korea; andKuhmo Petrochemical of Korea.

The base rubber may also comprise high or medium Mooney viscosityrubber, or blends thereof. A “Mooney” unit is a unit used to measure theplasticity of raw or unvulcanized rubber and is defined according toASTM D-1646. The Mooney viscosity range is preferably greater than about40, more preferably in the range from about 40 to 60 and most preferablyin the range from about 40 to 52.

Commercial sources of suitable polybutadienes include Bayer AG CB23(Nd-catalyzed), which has a Mooney viscosity of around 50 and is ahighly linear polybutadiene, and CB1221 (Co-catalyzed). If desired, thepolybutadiene can also be mixed with other elastomers known in the art,such as other polybutadiene rubbers, natural rubber, styrene butadienerubber, and/or isoprene rubber in order to further modify the propertiesof the core. When a mixture of elastomers is used, the amounts of otherconstituents in the core composition are typically based on 100 parts byweight of the total elastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzedpolybutadiene, a rare earth-catalyzed polybutadiene rubber, or blendsthereof. If desired, the polybutadiene can also be mixed with otherelastomers known in the art such as natural rubber, polyisoprene rubberand/or styrene-butadiene rubber in order to modify the properties of thecore. Other suitable base rubbers include thermosetting materials suchas, ethylene propylene diene monomer rubber, ethylene propylene rubber,butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber,nitrile rubber, and silicone rubber.

Suitable peroxide initiating agents include dicumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy)hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene;1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butylhydroperoxide, c′-c′ bis(t-butylperoxy) diisopropylbenzene,di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butylperoxide. Preferably, the rubber composition includes from about 0.25 toabout 5.0 parts by weight peroxide per 100 parts by weight rubber (phr),more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. Ina most preferred embodiment, the peroxide is present in an amount ofabout 0.8 phr. These ranges of peroxide are given assuming the peroxideis 100% active, without accounting for any carrier that might bepresent. Because many commercially available peroxides are sold alongwith a carrier compound, the actual amount of active peroxide presentmust be calculated. Commercially-available peroxide initiating agentsinclude DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals).Similar initiating agents are available from AkroChem, Lanxess,Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available andpreferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, whichis a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi(2-t-butylperoxyisopropyl) benzene. TRIGONOX™ peroxides are generallysold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal saltsof diacrylates, dimethacrylates, and monomethacrylates suitable for usein this invention include those wherein the metal is zinc, magnesium,calcium, barium, tin, aluminum, lithium, sodium, potassium, iron,zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but thepresent invention is not limited thereto. ZDA provides golf balls with ahigh initial velocity. The ZDA can be of various grades of purity. Forthe purposes of this invention, the lower the quantity of zinc stearatepresent in the ZDA the higher the ZDA purity. ZDA containing less thanabout 10% zinc stearate is preferable. More preferable is ZDA containingabout 4-8% zinc stearate. Suitable, commercially available zincdiacrylates include those from Sartomer Co. The preferred concentrationsof ZDA that can be used are about 10 phr to about 40 phr, morepreferably 20 phr to about 35 phr, most preferably 25 phr to about 35phr. In a particularly preferred embodiment, the reactive co-agent ispresent in an amount of about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combinationwith those mentioned above include, but are not limited to,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, andthe like. It is understood by those skilled in the art, that in the casewhere these co-agents may be liquids at room temperature, it may beadvantageous to disperse these compounds on a suitable carrier topromote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidativebreakdown of elastomers, and/or inhibit or prevent reactions that arepromoted by oxygen radicals. Some exemplary antioxidants that may beused in the present invention include, but are not limited to, quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants. A preferred antioxidant is2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPCfrom R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T,VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Suitable antioxidants include, but are not limited to,alkylene-bis-alkyl substituted cresols; substituted phenols; alkylenebisphenols; and alkylene trisphenols. The antioxidant is typicallypresent in an amount of about 0.1 phr to 5 phr, preferably from about0.1 phr to 2 phr, more preferably about 0.1 phr to 1 phr. In analternative embodiment, the antioxidant should be present in an amountto ensure that the hardness gradient of the core layers is “negative.”Preferably, about 0.2 phr to 1 phr antioxidant is added to the corelayer formulation, more preferably, about 0.3 to 0.8 phr, and mostpreferably 0.4 to 0.7 phr. Preferably, about 0.25 phr to 1.5 phr ofperoxide as calculated at 100% active can be added to the coreformulation, more preferably about 0.5 phr to 1.2 phr, and mostpreferably about 0.7 phr to 1.0 phr. The ZDA amount can be varied tosuit the desired compression, spin and feel of the resulting golf ball.The cure regime can have a temperature range from about 290° F. to 350°F., more preferably about 300° F. to 335° F., and the stock is held atthat temperature for about 10 minutes to 30 minutes.

The thermoset rubber compositions may also include an optional ‘soft andfast agent’. As used herein, “soft and fast agent” means any compound ora blend thereof that that is capable of making a core 1) be softer(lower compression) at constant COR or 2) have a higher COR at equalcompression, or any combination thereof, when compared to a coreequivalently prepared without a soft and fast agent. Preferably, thethermoset core layer compositions may contain about 0.05 phr to 10.0 phrsoft and fast agent. In one embodiment, the soft and fast agent ispresent in an amount of about 0.05 phr to 3.0 phr, preferably about 0.05phr to 2.0 phr, more preferably about 0.05 phr to 1.0 phr. In anotherembodiment, the soft and fast agent is present in an amount of about 2.0phr to 5.0 phr, preferably about 2.35 phr to 4.0 phr, and morepreferably about 2.35 phr to 3.0 phr. Suitable soft and fast agentsinclude, but are not limited to, organosulfur or metal-containingorganosulfur compounds, an organic sulfur compound, including mono, di,and polysulfides, a thiol, or mercapto compound, an inorganic sulfidecompound, a Group VIA compound, or mixtures thereof. The soft and fastagent component may also be a blend of an organosulfur compound and aninorganic sulfide compound.

Fillers may be added to the thermoset rubber layer compositionstypically include, but are not limited to, processing aids and/orcompounds to affect rheological and mixing properties, density-modifyingfillers, tear strength, or reinforcement fillers, and the like. Fillersinclude materials such as tungsten, zinc oxide, barium sulfate, silica,calcium carbonate, zinc carbonate, metals, metal oxides and salts,regrind (recycled core material typically ground to about 30 meshparticle size), high-Mooney-viscosity rubber regrind, trans-rubberregrind (recycled core material containing high trans isomer ofpolybutadiene), and the like. When trans-regrind is present, the amountof trans isomer is preferably between about 10% and 60%. The fillers aregenerally inorganic and suitable fillers include numerous metals ormetal oxides, such as zinc oxide and tin oxide, as well as bariumsulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, an array of silicas, and mixtures thereof.Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Fillers mayinclude polymeric, ceramic, metal, and glass microspheres may be solidor hollow, and filled or unfilled. Fillers may be added to one or morelayers of the golf ball to modify the density thereof.

The thermoset rubber shell and/or core layers may optionally include atleast one additive and/or filler. These materials are also suitable forinclusion in the thermoplastic layers of the present invention. Suitableadditives and fillers include, but are not limited to, chemical blowingand foaming agents, optical brighteners, coloring agents, fluorescentagents, whitening agents, UV absorbers, light stabilizers, defoamingagents, processing aids, antioxidants, stabilizers, softening agents,fragrance components, plasticizers, impact modifiers, TiO₂, acidcopolymer wax, surfactants, performance additives (e.g., A-C performanceadditives, particularly A-C low molecular weight ionomers andcopolymers, A-C oxidized polyethylenes, and A-C ethylene vinyl acetatewaxes, commercially available from Honeywell International Inc.), fattyacid amides (e.g., ethylene bis-stearamide and ethylene bis-oleamide),fatty acids and salts thereof (e.g., stearic acid, oleic acid, zincstearate, magnesium stearate, zinc oleate, and magnesium oleate), andfillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate,calcium oxide, calcium carbonate, zinc carbonate, barium carbonate,tungsten, tungsten carbide, silica, lead silicate, regrind, clay, mica,talc, nano-fillers, carbon black, glass flake, milled glass, flock,fibers, and mixtures thereof. Suitable additives are more fullydescribed in, U.S. Pat. No. 7,041,721 which issued on May 9, 2006, thedisclosure of which is hereby incorporated herein by reference. In aparticular embodiment, the total amount of additive(s) and filler(s)present in the particle composition is 20 wt % or less, or 15 wt % orless, or 12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt% or less, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, orwithin a range having a lower limit of 0 or 2 or 3 or 5 wt %, based onthe total weight of the particle composition, and an upper limit of 9 or10 or 12 or 15 or 20 wt %, based on the total weight of the particlecomposition. In a particular aspect of this embodiment, the particlecomposition includes fillers selected from carbon black, micro- andnano-scale clays and organoclays, including (e.g., CLOISITE and NANOFILnanoclays, commercially available from Southern Clay Products, Inc.;NANOMAX and NANOMER nanoclays, commercially available from Nanocor,Inc., and PERKALITE nanoclays, commercially available from Akzo NobelPolymer Chemicals), micro- and nano-scale talcs (e.g., LUZENAC HAR highaspect ratio talcs, commercially available from Luzenac America, Inc.),glass (e.g., glass flake, milled glass, microglass, and glass fibers),micro- and nano-scale mica and mica-based pigments (e.g., IRIODIN pearlluster pigments, commercially available from The Merck Group), andcombinations thereof. Particularly suitable combinations of fillersinclude, but are not limited to, micro-scale fillers combined withnano-scale fillers, and organic fillers with inorganic fillers. For thethermoset rubber layers of the invention, the fillers and/or additivesare present in an amount of about 50 wt % or less, preferably 30 wt % orless, more preferably 20 wt % or less, and most preferably 15 wt % orless, based on the total weight of the composition. Alternatively, forthe thermoplastic layers of the invention, the fillers and/or additivesare present in an amount of about 10 wt % or less, more preferably 6 wt% or less, and most preferably 3 wt % or less, based on the total weightof the composition.

The particle composition optionally includes one or more melt flowmodifiers. Suitable melt flow modifiers include materials which increasethe melt flow of the composition, as measured using ASTM D-1238,condition E, at 190° C., using a 2160-g weight. Examples of suitablemelt flow modifiers include, but are not limited to, fatty acids andfatty acid salts, including, but not limited to, those disclosed in U.S.Pat. No. 5,306,760, the disclosure of which is hereby incorporatedherein by reference; fatty amides and salts thereof; polyhydricalcohols, including, but not limited to, those disclosed in U.S. Pat.Nos. 7,365,128 and 8,163,823, the entire disclosures of which are herebyincorporated herein by reference; polylactic acids, including, but notlimited to, those disclosed in U.S. Pat. No. 7,642,319, the disclosureof which is hereby incorporated herein by reference; and the modifiersdisclosed in U.S. Pat. No. 8,163,823 and U.S. Patent ApplicationPublication No. 2009/0203469, the disclosures of which are herebyincorporated herein by reference. Flow enhancing additives also include,but are not limited to, montanic acids, esters of montanic acids andsalts thereof, bis-stearoylethylenediamine, mono- and polyalcohol esterssuch as pentaerythritol tetrastearate, zwitterionic compounds, andmetallocene-catalyzed polyethylene and polypropylene wax, includingmaleic anhydride modified versions thereof, amide waxes and alkylenediamides such as bistearamides. Particularly suitable fatty amidesinclude, but are not limited to, saturated fatty acid monoamides (e.g.,lauramide, palmitamide, arachidamide behenamide, stearamide, and12-hydroxy stearamide); unsaturated fatty acid monoamides (e.g.,oleamide, erucamide, and ricinoleamide); N-substituted fatty acid amides(e.g., N-stearyl stearamide, N-behenyl behenamide, N-stearyl behenamide,N-behenyl stearamide, N-oleyl oleamide, N-oleyl stearamide, N-stearyloleamide, N- stearyl erucamide, erucyl erucamide, and erucyl stearamide,N-oleyl palmitamide, methylol amide (more preferably, methylolstearamide, methylol behenamide); saturated fatty acid bis-amides (e.g.,methylene bis-stearamide, ethylene bis-stearamide, ethylenebis-isostearamide, ethylene bis-hydroxystearamide, ethylenebis-behenamide, hexamethylene bis-stearamide, hexamethylenebis-behenamide, hexamethylene bis-hydroxystearamide, N,N′-distearyladipamide, and N,N′-distearyl sebacamide); unsaturated fatty acidbis-amides (e.g., ethylene bis-oleamide, hexamethylene bis-oleamide,N,N′-dioleyl adipamide, N,N′-dioleyl sebacamide); and saturated andunsaturated fatty acid tetra amides, stearyl erucamide, ethylene bisstearamide and ethylene bis oleamide. Suitable examples of commerciallyavailable fatty amides include, but are not limited to, KEMAMIDE fattyacids, such as KEMAMIDE B (behenamide/arachidamide), KEMAMIDE W40(N,N′-ethylenebisstearamide), KEMAMIDE P181 (oleyl palmitamide),KEMAMIDE S (stearamide), KEMAMIDE U (oleamide), KEMAMIDE E (erucamide),KEMAMIDE 0 (oleamide), KEMAMIDE W45 (N,N′-ethylenebisstearamide),KENAMIDE W20 (N,N′-ethylenebisoleamide), KEMAMIDE E180 (stearylerucamide), KEMAMIDE E221 (erucyl erucamide), KEMAMIDE S180 (stearylstearamide), KEMAMIDE S221 (erucyl stearamide), commercially availablefrom Chemtura Corporation; and CRODAMIDE fatty amides, such as CRODAMIDEOR (oleamide), CRODAMIDE ER (erucamide), CRODAMIDE SR (stereamide),CRODAMIDE BR (behenamide), CRODAMIDE 203 (oleyl palmitamide), andCRODAMIDE 212 (stearyl erucamide), commercially available from CrodaUniversal Ltd.

The shell layer, and intermediate and outer core layers of the hollowgolf ball may also be formed from thermoplastic materials such asionomeric polymers, and highly- and fully-neutralized ionomers (HNP).Acid moieties of the HNP's, typically ethylene-based ionomers, arepreferably neutralized greater than about 80%, more preferably greaterthan about 90%, and most preferably about 100%. The HNP's can be also beblended with a second polymer component, which, if containing an acidgroup, may be neutralized in a conventional manner, by the organic fattyacids of the present invention, or both. The second polymer component,which may be partially- or fully-neutralized, preferably comprisesionomeric copolymers and terpolymers, ionomer precursors,thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes,polyureas, thermoplastic elastomers, polybutadiene rubber, balata,metallocene-catalyzed polymers (grafted and non-grafted), single-sitepolymers, high-crystalline acid polymers, cationic ionomers, and thelike. HNP polymers typically have a material hardness of between about20 and about 80 Shore D, and a flexural modulus of between about 3,000psi and about 200,000 psi.

Preferably, the HNP's are ionomers and/or their acid precursors that arepreferably neutralized, either fully or partially, with organic acidcopolymers or the salts thereof. The acid copolymers are preferablyα-olefin, such as ethylene, C₃₋₈ α,β-ethylenically unsaturatedcarboxylic acid, such as acrylic and methacrylic acid, copolymers. Theymay optionally contain a softening monomer, such as alkyl acrylate andalkyl methacrylate, wherein the alkyl groups have from 1 to 8 carbonatoms.

The acid copolymers can be described as E/X/Y copolymers where E isethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Yis a softening comonomer. In a preferred embodiment, X is acrylic ormethacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. Xis preferably present in an amount from about 1 to about 35 weightpercent of the polymer, more preferably from about 5 to about 30 weightpercent of the polymer, and most preferably from about 10 to about 20weight percent of the polymer. Y is preferably present in an amount fromabout 0 to about 50 weight percent of the polymer, more preferably fromabout 5 to about 25 weight percent of the polymer, and most preferablyfrom about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are notlimited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containingethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylatecopolymers. The most preferred acid-containing ethylene copolymers are,ethylene/(meth) acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylicacid/ethyl acrylate, and ethylene/(meth) acrylic acid/methyl acrylatecopolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na,Mg, K, Ca, or Zn.

It has been found that by adding sufficient organic acid or salt oforganic acid, along with a suitable base, to the acid copolymer orionomer, however, the ionomer can be neutralized, without losingprocessability, to a level much greater than for a metal cation.Preferably, the acid moieties are neutralized greater than about 80%,preferably from 90-100%, most preferably 100% without losingprocessability. This accomplished by melt-blending an ethyleneα,β-ethylenically unsaturated carboxylic acid copolymer, for example,with an organic acid or a salt of organic acid, and adding a sufficientamount of a cation source to increase the level of neutralization of allthe acid moieties (including those in the acid copolymer and in theorganic acid) to greater than 90%, (preferably greater than 100%).

The organic acids are typically aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. The salts of organic acids ofthe present invention include the salts of barium, lithium, sodium,zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, salts of fatty acids, particularly stearic, behenic, erucic,oleic, linoelic or dimerized derivatives thereof. It is preferred thatthe organic acids and salts of the present invention be relativelynon-migratory (they do not bloom to the surface of the polymer underambient temperatures) and non-volatile (they do not volatilize attemperatures required for melt-blending).

The ionomers of the invention may also be more conventional ionomers,i.e., partially-neutralized with metal cations. The acid moiety in theacid copolymer is neutralized about 1 to about 90%, preferably at leastabout 20 to about 75%, and more preferably at least about 40 to about70%, to form an ionomer, by a cation such as lithium, sodium, potassium,magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixturethereof.

Preferred thermoplastic materials are disclosed in U.S. Pat. No.7,591,742, the disclosure of which is incorporated herein in itsentirety by reference thereto. Thermoplastic elastomers (TPE) many alsobe used for the thermoplastic shell or core layers and/or to modify theproperties of the shell and/or core layers, or the uncured rubber corelayer stock by blending with the base thermoset rubber. These TPEsinclude natural or synthetic balata, or high trans-polyisoprene, hightrans-polybutadiene, or any styrenic block copolymer, such as styreneethylene butadiene styrene, styrene-isoprene-styrene, etc., ametallocene or other single-site catalyzed polyolefin such asethylene-octene, or ethylene-butene, or thermoplastic polyurethanes(TPU), including copolymers, e.g. with silicone. Other suitable TPEs forblending with the thermoset rubbers of the present invention includePEBAX®, which is believed to comprise polyether amide copolymers,HYTREL®, which is believed to comprise polyether ester copolymers,thermoplastic urethane, and KRATON®, which is believed to comprisestyrenic block copolymers elastomers. Any of the TPEs or TPUs above mayalso contain functionality suitable for grafting, including maleic acidor maleic anhydride.

Additional polymers may also optionally be incorporated into the baserubber for the shell and core layers. Examples include, but are notlimited to, thermoset elastomers such as core regrind, thermoplasticvulcanizate, copolymeric ionomer, terpolymeric ionomer, polycarbonate,polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer(SAN) (including olefin-modified SAN andacrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydridecopolymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer, ethylene-vinyl acetate copolymers,polyurea, and polysiloxane or any metallocene-catalyzed polymers ofthese species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as C--caprolactam orΩ-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6, and NYLON 46.

The hollow interior of the shell layer has a diameter of about 0.1inches to about 1.1 inches, preferably about 0.2 inches to about 0.9inches, more preferably about 0.25 inches to about 0.75 inches, and mostpreferably about 0.3 inches to about 0.5 inches. In one preferredembodiment, the hollow interior of the shell layer has a diameter ofgreater than 0.5 inches. The shell layer has a thickness that rangesfrom 0.01 inches to about 0.4 inches. When the shell layer is desired tobe relatively thick, the shell layer thickness is about 0.125 inches toabout 0.375 inches, preferably about 0.2 inches to about 0.3125 inches,more preferably about 0.25 inches to about 0.3 inches, and mostpreferably about 0.26 inches to about 0.275 inches. When the shell layeris desired to be relatively thin, the shell layer thickness is about0.01 inches to about 0.1 inches, preferably about 0.02 inches to about0.075 inches, more preferably about 0.025 inches to about 0.04 inches,and most preferably about 0.03 inches to about 0.035 inches. When theshell layer is relatively thin and formed from a thermoplastic material,the TP material is preferably selected to be somewhat heat resistant (orblended with a heat resistant TP material) to avoid melting of the layerby subsequent molding of additional core and/or cover layers.

With the dimensions of the hollow interior in mind, the hollow cores(shell layer, shell layer and outer core layer(s)) of the inventionpreferably have an outer diameter of about 0.75 inches to about 1.58inches, preferably about 1.0 inches to about 1.57 inches, morepreferably about 1.3 inches to about 1.56 inches, and most preferablyabout 1.4 inches to about 1.55 inches. In preferred embodiments, theshell layer has an outer diameter of about 0.75 inches, 1.0 inches, 1.20inches, or 1.30 inches, with a most preferred outer diameter being 0.75inches or 1.0 inches. In an alternative embodiment, the outer core layershould have an outer diameter (the entire hollow core, shell layer plusouter core layer) of about 1.30 inches to about 1.62 inches, preferably1.4 inches to about 1.6 inches, and more preferably about 1.5 inches toabout 1.59 inches. In preferred embodiments, the outer core layer has anouter diameter of about 1.51 inches, 1.53 inches, or most preferably1.550 inches.

The inner and outer cover layers preferably have a thickness of about0.010 to 0.080 inches, more preferably about 0.015 to 0.060 inches, andmost preferably about 0.020 to 0.040 inches. Alternatively, the innerand outer cover layers have a thickness of about 0.015 inches to about0.055 inches, more preferably about 0.02 inches to about 0.04 inches,and most preferably about 0.025 inches to about 0.035 inches. The innercover layer, if present, preferably has a hardness of about 60 Shore Dor greater, more preferably about 65 Shore D or greater, and mostpreferably about 70 Shore D or greater. The inner cover layer ispreferably harder than the outer cover layer although in one embodimentthe outer cover layer is harder than the inner cover layer. The outercover layer preferably has a hardness of about 60 Shore D or less, morepreferably about 55 Shore D or less, and most preferably about 50 ShoreD or less.

Formation of the shell and outer core layers of the invention may beaccomplished in a variety of ways, such as those disclosed in U.S. Pat.Nos. 5,480,155; 6,315,683, and 8,262,508, the disclosures of which areincorporated herein, in their entirety, by reference thereto.

The golf ball of the present invention includes a hollow core which isformed from a shell layer that contains a spherical hollow portion inits interior. The spherical inner core shell layer is formed from athermoplastic composition, preferably a conventional ionomer or afully-neutralized ionomer. The shell layer has an outer surface, aninner surface, and an inner diameter that define the dimensions of thehollow center. A single thermoplastic outer core layer is formed overthe shell layer and preferably includes an ionomeric composition. Thecombination of the thermoplastic shell layer and the thermoplastic outercore layer results in a TP/TP hollow core. Typically, an inner coverlayer and an outer cover layer are formed over the thermoplastic outercore layer. In a preferred embodiment, the inner cover includes anionomeric material and the outer cover includes a polyurea or, morepreferably, a polyurethane. The outer cover is preferably softer thanthe inner cover layer.

The hollow center has a diameter of about 0.15 to 1.1 inches, preferablyabout 0.25 to 1.0 inches, more preferably about 0.25 to 0.75 inches, andmost preferably about 0.3 to 0.5 inches. The surface hardness of thethermoplastic shell layer is preferably greater than the hardness of theinner surface of the shell layer by about 0 to 5 Shore C to define ahardness gradient. The thermoplastic outer core layer also has ahardness gradient, which is the same as or greater than the hardnessgradient of the thermoplastic shell layer. In an alternative embodiment,the hardness gradient of the thermoplastic outer core layer has a ‘zerohardness gradient’. The zero hardness gradient is typically about 0Shore C (defined herein as ±2 Shore C). The hardness gradient of thethermoplastic outer core layer may also have a ‘negative hardnessgradient’, preferably about 1 to 10 Shore C, more preferably about 2 to8 Shore C, and most preferably about 3 to 5 Shore C. The hardnessgradient of the thermoplastic outer core layer may also have a ‘positivehardness gradient’, preferably about 1 to 10 Shore C, more preferablyabout 2 to 8 Shore C, and most preferably about 3 to 5 Shore C.

The golf ball has a first volume and the hollow center has a secondvolume. The volume of the hollow center is about 2% to 30% of the golfball volume, more preferably about 5% to 25% of the golf ball volume,and most preferably about 10% to 20% of the golf ball volume.

The thermoplastic inner core shell layer has a COR less than about 0.750when measured at an incoming velocity of 125 ft/s. Preferably, the CORis less than about 0.700, more preferably about 0.500 to 0.700, and mostpreferably about 0.600 to 0.700. The overall hollow core (thecombination of the thermosplastic shell layer and the thermoplasticouter core layer has a COR, measured at an incoming velocity of 125ft/s, higher than the COR of the inner core shell layer by greater thanabout 5%, more preferably about 10 to 50%, and most preferably about 15to 30%.

Referring to FIGS. 1 a and 1 b, two different embodiments of the TP/TPhollow core golf ball are disclosed. FIG. 1 a depicts a hardness profilefor a golf ball having a hollow core, an ionomer inner cover layer, anda polyurethane outer cover layer. The thermoplastic shell layer has athickness of about 0.375 inches and an outer diameter of about 1.0inches, and the spherical hollow interior has a diameter of about 0.25inches. The thermoplastic outer core layer has a thickness of about0.275 inches and an outer diameter of about 1.55 inches. The inner coverlayer has a thickness of about 0.035 inches and the outer cover layerhas a thickness of about 0.03 inches. Both the thermoplastic shell layerand the thermoplastic outer core layer have a ‘zero hardness gradient’across their respective thickness. FIG. 1 b depicts a hardness profilefor another golf ball having a hollow core, an ionomer inner coverlayer, and a polyurethane outer cover layer. The thermoplastic shelllayer has a thickness of about 0.3125 inches and an outer diameter ofabout 0.75 inches, and the spherical hollow interior has a diameter ofabout 0.125 inches. The thermoplastic outer core layer has a thicknessof about 0.39 inches and an outer diameter of about 1.53 inches. Theinner cover layer has a thickness of about 0.045 inches and the outercover layer has a thickness of about 0.03 inches. Both the thermoplasticshell layer and the thermoplastic outer core layer have a ‘zero hardnessgradient’ across their respective thickness.

In a another embodiment of the invention, the shell layer is formed froma thin, relatively stiff and hard thermoplastic composition, preferablycovered by a thermoplastic or thermoset outer core layer, mostpreferably by a thermoplastic outer core layer.

Preferred materials for use in the shell layers include acid copolymers,described as E/X copolymers or E/X/Y terpolymers where E is ethylene, Xis an α,β-ethylenically unsaturated carboxylic acid, and Y is asoftening comonomer. In a preferred embodiment, X is acrylic ormethacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. Xis preferably present in an amount from about 1 to about 35 weightpercent of the polymer, more preferably from about 5 to about 30 weightpercent of the polymer, and most preferably from about 10 to about 20weight percent of the polymer. Y is preferably present in an amount fromabout 0 to about 15 weight percent of the polymer, more preferably fromabout 0 to about 10 weight percent of the polymer, and most preferablyfrom about 0 to about 5 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are notlimited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containingethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylatecopolymers. The most preferred acid-containing ethylene copolymers are,ethylene/(meth) acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylicacid/ethyl acrylate, and ethylene/(meth) acrylic acid/methyl acrylatecopolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na,Mg, K, Ca, or Zn. It has been found that by adding sufficient organicacid or salt of organic acid, along with a suitable base, to the acidcopolymer or ionomer, however, the ionomer can be neutralized, withoutlosing processability, to a level much greater than for a metal cation.Preferably, the acid moieties are neutralized greater than about 80%,preferably from 90-100%, most preferably 100% without losingprocessability. This accomplished by melt-blending an ethyleneα,β-ethylenically unsaturated carboxylic acid copolymer, for example,with an organic acid or a salt of organic acid, and adding a sufficientamount of a cation source to increase the level of neutralization of allthe acid moieties (including those in the acid copolymer and in theorganic acid) to greater than 90%, (preferably greater than 100%). Theionomers of the invention may also be more conventional ionomers, i.e.,partially-neutralized with metal cations. The acid moiety in the acidcopolymer is neutralized about 1 to about 90%, preferably at least about20 to about 75%, and more preferably at least about 40 to about 70%, toform an ionomer, by a cation such as lithium, sodium, potassium,magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixturethereof. Preferred ionomers are the hard, high-acid ionomers.

Thermoplastic elastomers (TPE) many also be used for the thermoplasticshell or core layers and/or to modify the properties of the shell and/orcore layers, or the uncured rubber core layer stock by blending with thebase thermoset rubber. These TPEs include natural or synthetic balata,or high trans-polyisoprene, high trans-polybutadiene, or any styrenicblock copolymer, such as styrene ethylene butadiene styrene,styrene-isoprene-styrene, etc., a metallocene or other single-sitecatalyzed polyolefin such as ethylene-octene, or ethylene-butene, orthermoplastic polyurethanes (TPU), including copolymers, e.g. withsilicone. Other suitable TPEs for blending with the thermoset rubbers ofthe present invention include PEBAX®, which is believed to comprisepolyether amide copolymers, HYTREL®, which is believed to comprisepolyether ester copolymers, thermoplastic urethane, and KRATON®, whichis believed to comprise styrenic block copolymers elastomers. PreferredPEBAX® materials include PEBAX® 5533, PEBAX®6333, PEBAX®7033, andPEBAX®7233, commercially-available from DuPont. Another preferredmaterial is HYTREL® 6356.

Suitable polyamides for use in shell layer compositions include resinsobtained by: (1) polycondensation of (a) a dicarboxylic acid, such asoxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalicacid, or 1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such asethylenediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, or decamethylenediamine, 1,4-cyclohexanediamine,or m-xylylenediamine; (2) a ring-opening polymerization of cycliclactam, such as C--caprolactam or Ω-laurolactam; (3) polycondensation ofan aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoicacid, 11-aminoundecanoic acid, or 12-aminododecanoic acid; or (4)copolymerization of a cyclic lactam with a dicarboxylic acid and adiamine. Specific examples of suitable polyamides include NYLON® 6,NYLON® 66, NYLON® 610, NYLON® 11, NYLON® 12, copolymerized NYLON®,NYLON® MXD6, and NYLON® 46.

The material used for the shell layers of the invention have aMelt-Volume Flow Rate (MVR) at 230° C./2.16 kg, per ISO test method1133, of about 5.0 cm³/10 min or less, more preferably about 3.0 cm³/10min or less, and most preferably about 1.0 cm³/10 min or less. In onepreferred embodiment, the material has a MVR of about 0.500 cm³/10 min.The shell layer has a hardness of about 55 Shore D or greater, morepreferably about 60 Shore D or greater, and most preferably about 65Shore D or greater. In a particularly preferred embodiment, the shelllayer is formed from a HYTREL® having a hardness of about 63 Shore D.

The shell layer preferably comprises an ionomer or non-ionomericpolyolefin, such as PE-(meth)acrylic acid, PE, PP, or EP copolymers,metallocene copolymers, polyesters, including HYTREL®, polyamides,including block polyamides, such as PEBAX®, and polycarbonate. Otherthermoplastics that have high melting temperatures, to facilitateovermolding, are also suitable for the inventive shell layers.

Some additional preferred polyolefin copolymers, such as polypropylenecopolymers, are disclosed in U.S. Pat. Nos. 8,017,204; 7,339,018,7,304,111; 6,765,068; and 6,342,564, and EP Patent Application No.2586823 A1, which are incorporated herein by reference thereto. Suitablecommercially-available polypropylene impact copolymers include thosesold by LyondellBasell of the Netherlands under the tradenames Clyrell®,Adflex®, and Adstif®, as well as the impact copolymers and randomcopolymers sold by Braskem, USA.

In this preferred embodiment, the shell layer is encased with athermoplastic or a thermoset outer core layer, most preferably athermoplastic outer core layer. When the outer core layer is athermoplastic material, it is preferably a highly- or fully-neutralizedionomers (HNPs). Acid moieties of the HNP's, typically ethylene-basedionomers, are preferably neutralized greater than about 80%, morepreferably greater than about 90%, and most preferably about 100%. TheHNP's can be also be blended with a second polymer component, which, ifcontaining an acid group, may be neutralized in a conventional manner,by the organic fatty acids of the present invention, or both. The secondpolymer component, which may be partially- or fully-neutralized,preferably comprises ionomeric copolymers and terpolymers, ionomerprecursors, thermoplastics, polyamides, polycarbonates, polyesters,polyurethanes, polyureas, thermoplastic elastomers, polybutadienerubber, balata, metallocene-catalyzed polymers (grafted andnon-grafted), single-site polymers, high-crystalline acid polymers,cationic ionomers, and the like. HNP polymers typically have a materialhardness of between about 20 and about 80 Shore D, and a flexuralmodulus of between about 3,000 psi and about 200,000 psi. Preferably,the HNP's are ionomers and/or their acid precursors that are preferablyneutralized, either fully or partially, with organic acid copolymers orthe salts thereof. The acid copolymers are preferably a-olefin, such asethylene, C₃₋₈ α,β-ethylenically unsaturated carboxylic acid, such asacrylic and methacrylic acid, copolymers. They may optionally contain asoftening monomer, such as alkyl acrylate and alkyl methacrylate,wherein the alkyl groups have from 1 to 8 carbon atoms.

When the outer core layer is a thermoset material, it is preferablyformed from a polybutadiene rubber, such as those described above.

The TP or TS outer core layer has a hardness that is equal to or lessthan that of the shell layer, preferably at least about 2 Shore Csofter, more preferably about 5 Shore C softer, and most preferablyabout 10 Shore C softer. Alternatively, The TP or TS outer core layerhas a hardness that is equal to or less than that of the shell layer,preferably at least about 1 Shore D softer, more preferably about 3Shore D softer, and most preferably about 5 Shore D softer. The outercore layer has a thickness of about 0.045 inches to about 0.55 inches,more preferably about 0.10 inches to about 0.35 inches, and mostpreferably about 0.15 inches to about 0.25 inches.

One or more additional intermediate core layers may be disposed betweenthe shell layer and the outer core layer. Additionally, additionallayers may be disposed between the outer core layer and the coverlayer(s). The cover can be a single layer or have multiple layer, suchas an inner cover layer and an outer cover layer. Preferably the hollowcore is covered by a soft polyurethane outer cover layer having athickness of about 0.015 inches to about 0.045 inches and a hardness ofabout 58 Shore D or less, and an inner cover layer formed from arelatively hard ionomer material and having a thickness of about 0.015inches to about 0.065 inches and a hardness of at least 60 Shore D, morepreferably at least about 64 Shore D.

The shell layer can be blow-molded, rotationally-molded, gas-injectionmolded, etc. In extrusion blow molding, the shell layer is formed as aone-piece unit. Extrusion blow molding involves extruding a continuoustube of molten plastic, called a parison, vertically downward betweenshell mold halves. The two mold halves close, cutting the parison freefrom the extruder while pinching closed the top of the tube and sealingat the bottom around a blow pin. The parison is inflated withpressurized air injected into the mold through the blow pin, forcing themolten polymer against the mold inner surface and forming the hollowspherical shell. After cooling the mold is opened, the solidified partis removed, and the process is repeated. Another suitable process forforming the hollow shell layers of the present invention is rotationalmolding. The rotational molding process involves using gravity and heatto fuse together polymeric powder inside a rotating mold. The processbegins by adding to a split spherical cavity mold the appropriate amountof polymer powder to achieve the desired shell thickness.

The mold is heated to the melting point of the polymer whilecontinuously rotating it on two perpendicular axes, slowly melting thepolymer to form a fused shell layer of uniform thickness. The mold isthen cooled while maintaining rotation until the plastic solidifies andthe shell(s) can be removed from the open mold.

Both of these processes are used to make hollow, seamless parts out ofthermoplastic polymers. Rotational molding can also be used forthermosets. Blow molding is a molding process in which air pressure isused to inflate soft plastic into a mold cavity. It is an industrialprocess for making one-piece hollow plastic parts with thin walls, suchas the hollow shells of the present invention.

Blow molding is accomplished in two steps: (1) fabrication of a startingtube of molten plastic, called a parison (same as in glass-blowing); and(2) inflation of the tube to the desired final shape. Forming theparison is accomplished by either of two processes: extrusion orinjection molding. Extrusion blow molding consists of (1) extrusion ofparison; (2) parison is pinches at the top and sealed at the bottomaround a metal blow pin as the two halves of the mold come together; (3)the tube is inflated so that it takes the shape of the mold cavity; and(4) mold is opened to remove the solidified part. For injection blowmolding, (1) the parison is injection molded around a blowing rod; (2)injection mold is opened and parison is transferred to a blow mold; (3)soft polymer is inflated to conform to a blow mold; and (4) blow mold isopened and blown product is removed. In a variation of injection blowmolding, called stretch blow molding, the blowing rod extends downwardinto the injection molded parison during step 2, thus stretching thesoft plastic and creating a more favorable stressing of the polymer thanconventional injection blow molding or extrusion blow molding. Theresulting structure is more rigid, with better impact resistance.Stretch blow molding is also suitable for the present invention.

Rotational molding uses gravity inside a rotating mold to achieve ahollow form. Also called rotomolding, it is an alternative to blowmolding for making hollow shapes. It is used principally forthermoplastic polymers, but applications for thermosets and elastomersare becoming more common. The process consists of the following steps:(1) a predetermined amount of polymer is loaded into the cavity of asplit mold; (2) the mold is then heated and simultaneously rotated ontwo perpendicular axes, so that the polymer impinges on all internalsurfaces of the mold, gradually forming a fused layer of uniformthickness; (3) while still rotating, the mold is cooled so that theplastic skin solidifies; and (4) the mold is opened, and the part isunloaded. Rotational speeds used in the process are relatively slow. Itis gravity, not centrifugal force, that causes uniform coating of themold surfaces.

Molds in rotational molding are simple and inexpensive compared toinjection molding or blow molding, but the production cycle is muchlonger, lasting perhaps ten minutes or more. To balance these advantagesand disadvantages in production, rotational molding is often performedon a multi-cavity indexing machine in which the multiple molds areworking simultaneously. One workstation may be an unload-load stationwhere the finished part is unloaded from the mold, and the polymer forthe next part is loaded into the cavity. Another station may consist ofa heating chamber, such as an oven, where hot-air convection heats themold while it is simultaneously rotated. Temperatures inside the chamberare typically about 400° F. to 850° F., depending on the polymer and theitem being molded. The final station may cool the mold, using forcedcold air or water spray, to cool and solidify the plastic moldinginside.

The shell layers (and, therefore, the hollow center), may also be formedfrom joining two premolded half shells.

The shell layer has a hardness of about 85 Shore C or greater, morepreferably about 90 Shore C or greater, and most preferably about 95Shore C or greater. Alternatively, the shell layer has a hardness ofabout 55 Shore D or greater, more preferably about 60 Shore D orgreater, and most preferably about 65 Shore D or greater. The materialof the shell layer preferably has a flexural modulus of greater thanabout 50,000 psi, more preferably greater than about 75,000 psi, andmost preferably greater than about 90,000 psi.

In any of these embodiments, the shell layer may be filled to increaseits specific gravity or the shell layer may be foamed (chemically orphysically) or otherwise reduced in specific gravity, including by‘filling’ the shell layer with glass or polymeric spheres, microspheres,microbeads, or foamed particulates, as examples. Any of theaforementioned methods of molding would be suitable for forming foamedor filled shell layers. A preferred foamed composition comprises athermosetting polyurethane foamed to a specific gravity of about 95% toabout 40% of the unfoamed specific gravity. Thermoplastic materials maybe extrusion foamed into sheets, which are then compression molded orvacuum formed into half shells. Thermoplastics may also be injectionmolded as a foam directly into half shells and then assembled intospheres. The foaming may alternatively be carried out during blowmolding or rotational molding in a one-step process. In one uniqueembodiment, the foamed layer shells have a ‘U-shaped’ hardness gradient,with the internal and external surfaces being higher in hardness thanthe foamed interior hardness.

A preferred shell would include two half shells of a foamedthermoplastic polymer joined to form a hollow sphere by a secondary stepof adhesion, spin bonding, ultrasonic bonding, or heat or solventwelding, as examples.

In another embodiment of the invention, the hollow core further includesa thermoplastic intermediate core layer disposed between thethermoplastic shell layer and the thermoplastic outer core layer. Instill another embodiment, the hollow core further includes a thermosetintermediate core layer disposed between the thermoplastic shell layerand the thermoplastic outer core layer. The intermediate core layer ispreferably formed from a thermoset rubber composition. In theseembodiments, the hollow center preferably has a diameter of about 0.15to 1.1 inches, the thermoplastic shell layer has a surface hardnessgreater than an inner surface hardness by about 1 to 10 Shore C todefine a hardness gradient, preferably a ‘positive hardness gradient’.The thermoplastic outer core layer preferably has a hardness gradientthat is different from the hardness gradient of the thermoplastic shelllayer or the intermediate layer.

The hollow core of the present invention is covered by at least onecover layer. An intermediate layer, such as an inner cover layer, mayoptionally be disposed about the hollow core, with the cover layerformed around the intermediate layer as an outer cover layer. While anyof the thermoplastic materials disclosed herein may be suitable for theinner or outer cover layers of the invention, in a preferred embodimentthe outermost cover is formed from a castable polyurea or a castablepolyurethane; castable hybrid poly(urethane/urea); and castable hybridpoly(urea/urethane). Suitable polyurethanes include those disclosed inU.S. Pat. Nos. 5,334,673 and 6,506,851. Suitable polyureas include thosedisclosed in U.S. Pat. Nos. 5,484,870 and 6,835,794. These patents areincorporated herein by reference thereto. Other suitable polyurethanecompositions comprise a reaction product of at least one polyisocyanateand at least one curing agent. The curing agent can include, forexample, one or more polyamines, one or more polyols, or a combinationthereof. The polyisocyanate can be combined with one or more polyols toform a prepolymer, which is then combined with the at least one curingagent. Thus, the polyols described herein are suitable for use in one orboth components of the polyurethane material, i.e., as part of aprepolymer and in the curing agent. More suitable polyurethanes aredescribed in U.S. Pat. No. 7,331,878, which is incorporated by referencein its entirety.

Any polyisocyanate available to one of ordinary skill in the art issuitable for use according to the invention. Exemplary polyisocyanatesinclude, but are not limited to, 4,4′-diphenylmethane diisocyanate(MDI); polymeric MDI; carbodiimide-modified liquid MDI;4,4′-dicyclohexylmethane diisocyanate (H12MDI); p-phenylene diisocyanate(PPDI); m-phenylene diisocyanate (MPDI); toluene diisocyanate (TDI);3,3′-dimethyl-4,4′-biphenylene diisocyanate; isophoronediisocyanate;1,6-hexamethylene diisocyanate (HDI); naphthalene diisocyanate; xylenediisocyanate; p-tetramethylxylene diisocyanate; m-tetramethylxylenediisocyanate; ethylene diisocyanate; propylene-1,2-diisocyanate;tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate;dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate; tetracene diisocyanate;napthalene diisocyanate; anthracene diisocyanate; isocyanurate oftoluene diisocyanate; uretdione of hexamethylene diisocyanate; andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g.,di-isocyanate, tri-isocyanate, and tetra-isocyanate. Preferably, thepolyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and morepreferably, the polyisocyanate includes MDI. It should be understoodthat, as used herein, the term MDI includes 4,4′-diphenylmethanediisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, andmixtures thereof and, additionally, that the diisocyanate employed maybe “low free monomer,” understood by one of ordinary skill in the art tohave lower levels of “free” monomer isocyanate groups, typically lessthan about 0.1% free monomer isocyanate groups. Examples of “low freemonomer” diisocyanates include, but are not limited to Low Free MonomerMDI, Low Free Monomer TDI, and Low Free Monomer PPDI. The at least onepolyisocyanate should have less than about 14% unreacted NCO groups.

Preferably, the at least one polyisocyanate has no greater than about8.0% NCO, more preferably no greater than about 7.8%, and mostpreferably no greater than about 7.5% NCO with a level of NCO of about7.2 or 7.0, or 6.5% NCO commonly used.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in thepolyurethane material. Suitable polyester polyols include, but are notlimited to, polyethylene adipate glycol; polybutylene adipate glycol;polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol;poly(hexamethylene adipate) glycol; and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polycaprolactone polyols include,but are not limited to, 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, polycarbonate polyols are included in thepolyurethane material of the invention. Suitable polycarbonates include,but are not limited to, polyphthalate carbonate and poly(hexamethylenecarbonate) glycol. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups. In one embodiment, the molecular weight of the polyol is fromabout 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethanecomposition of the invention and have been found to improve cut, shear,and impact resistance of the resultant balls.

Preferred polyamine curatives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline; m-phenylenediamine;4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-methylene-bis-(2,3-dichloroaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane; 2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE® 300, commercially available fromAlbermarle Corporation of Baton Rouge, La. Suitable polyamine curatives,which include both primary and secondary amines, preferably havemolecular weights ranging from about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curativesmay be added to the aforementioned polyurethane composition. Suitablediol, triol, and tetraol groups include ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; polypropylene glycol;lower molecular weight polytetramethylene ether glycol;1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy] ethoxy} benzene;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol;resorcinol-di-(β-hydroxyethyl) ether; hydroquinone-di-(β-hydroxyethyl)ether; and mixtures thereof. Preferred hydroxy-terminated curativesinclude 1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy] benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy] ethoxy}benzene; 1,4-butanediol, and mixtures thereof. Preferably, thehydroxy-terminated curatives have molecular weights ranging from about48 to 2000. It should be understood that molecular weight, as usedherein, is the absolute weight average molecular weight and would beunderstood as such by one of ordinary skill in the art.

Both the hydroxy-terminated and amine curatives can include one or moresaturated, unsaturated, aromatic, and cyclic groups. Additionally, thehydroxy-terminated and amine curatives can include one or more halogengroups. The polyurethane composition can be formed with a blend ormixture of curing agents. If desired, however, the polyurethanecomposition may be formed with a single curing agent.

In a preferred embodiment of the present invention, saturatedpolyurethanes are used to form one or more of the cover layers,preferably the outer cover layer, and may be selected from both castablethermoset and thermoplastic polyurethanes. In this embodiment, thesaturated polyurethanes of the present invention are substantially freeof aromatic groups or moieties. Saturated polyurethanes suitable for usein the invention are a product of a reaction between at least onepolyurethane prepolymer and at least one saturated curing agent. Thepolyurethane prepolymer is a product formed by a reaction between atleast one saturated polyol and at least one saturated diisocyanate. Asis well known in the art, that a catalyst may be employed to promote thereaction between the curing agent and the isocyanate and polyol, or thecuring agent and the prepolymer.

Additionally, polyurethane can be replaced with or blended with apolyurea material. Polyureas are distinctly different from polyurethanecompositions. The polyurea-based compositions are preferably saturatedin nature. The polyurea compositions may be formed from the reactionproduct of an isocyanate and polyamine prepolymer crosslinked with acuring agent. For example, polyurea-based compositions of the inventionmay be prepared from at least one isocyanate, at least one polyetheramine, and at least one diol curing agent or at least one diamine curingagent.

While any of the embodiments herein may have any known dimple number andpattern, a preferred number of dimples is 252 to 456, and morepreferably is 330 to 392. The dimples may comprise any width, depth, andedge angle disclosed in the prior art and the patterns may comprisesmultitudes of dimples having different widths, depths and edge angles.The parting line configuration of said pattern may be either a straightline or a staggered wave parting line (SWPL). Most preferably the dimplenumber is 330, 332, or 392 and comprises 5 to 7 dimples sizes and theparting line is a SWPL. In any of these embodiments the single-layercore may be replaced with a 2 or more layer core wherein at least onecore layer has a negative hardness gradient. Other than in the operatingexamples, or unless otherwise expressly specified, all of the numericalranges, amounts, values and percentages such as those for amounts ofmaterials and others in the specification may be read as if prefaced bythe word “about” even though the term “about” may not expressly appearwith the value, amount or range. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objective stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. Therefore, it will be understood that theappended claims are intended to cover all such modifications andembodiments, which would come within the spirit and scope of the presentinvention.

What is claimed is:
 1. A golf ball comprising a hollow core, the golfball comprising: a spherical inner core shell layer formed from a stiffthermoplastic composition, the shell layer having an outer surface, aninner surface, and an inner diameter to define a hollow center; an outercore layer disposed about the shell layer, the outer core layercomprising a thermoset material; an inner cover layer disposed about theouter core layer, the inner cover comprising an ionomeric material andhaving a first hardness; and an outer cover layer disposed about theinner cover layer, the outer cover comprising a polyurea or apolyurethane and having a second hardness different from the first;wherein the hollow center has a diameter of about 0.15 to 1.1 inches,the thermoplastic inner core shell layer has a hardness of about 85Shore C or greater, and the stiff thermoplastic composition has a meltvolume flow rate of about 5.0 cm³/10 min or less at 230° C./2.16 kg. 2.The golf ball of claim 1, wherein the stiff thermoplastic compositionhas a melt volume flow rate of about 3.0 cm³/10 min or less at 230°C./2.16 kg.
 3. The golf ball of claim 2, wherein the stiff thermoplasticcomposition has a melt volume flow rate of about 1.0 cm³/10 min or lessat 230° C./2.16 kg.
 4. The golf ball of claim 1, wherein the stiffthermoplastic inner shell layer comprises two pre-molded half shells. 5.The golf ball of claim 1, wherein the stiff thermoplastic inner shelllayer is blow molded, rotationally molded, or gas injection molded. 6.The golf ball of claim 1, wherein the stiff thermoplastic compositionhas a hardness of about 90 Shore C or greater.
 7. The golf ball of claim1, wherein the outer core layer comprises a polybutadiene rubber and hasa hardness equal to or less than the shell layer hardness.
 8. The golfball of claim 1, wherein the outer core layer has a thickness of about0.025 inches to about 0.115 inches.
 9. The golf ball of claim 1, whereinthe golf ball further comprises an intermediate layer disposed betweenthe outer core layer and the inner cover layer, the intermediate layercomprising a thermoset or thermoplastic material.
 10. The golf ball ofclaim 1, wherein the second hardness is greater than the first.
 11. Thegolf ball of claim 1, wherein the first hardness is greater than thesecond.
 12. The golf ball of claim 1, wherein the golf ball has a firstvolume and the hollow center has a second volume that is about 2% to 30%of the first volume.
 13. The golf ball of claim 1, wherein the sphericalinner core shell layer has a coefficient of restitution less than about0.700 when measured at an incoming velocity of 125 ft/s.
 14. The golfball of claim 1, wherein the outer core layer has a coefficient ofrestitution, measured at an incoming velocity of 125 ft/s, higher thanthe coefficient of restitution, measured at an incoming velocity of 125ft/s, of the inner core shell layer by 10-50%.
 15. A golf ballcomprising a hollow core, the golf ball comprising: a spherical innercore shell layer formed from a stiff thermoplastic composition, theshell layer having an outer surface, an inner surface, and an innerdiameter to define a hollow center; an outer core layer disposed aboutthe shell layer, the outer core layer comprising a thermoplasticmaterial; an inner cover layer disposed about the outer core layer, theinner cover comprising an ionomeric material and having a firsthardness; and an outer cover layer disposed about the inner cover layer,the outer cover comprising a polyurea or a polyurethane and having asecond hardness different from the first; wherein the hollow center hasa diameter of about 0.15 to 1.1 inches, the thermoplastic inner coreshell layer has a hardness of about 85 Shore C or greater, and the stiffthermoplastic composition has a melt volume flow rate of about 5.0 orless cm³/10 min at 230° C./2.16 kg.
 16. The golf ball of claim 15,wherein the outer core layer comprises a highly-neutralized ionomer andhas a hardness equal to or less than the shell layer hardness.
 17. Thegolf ball of claim 15, wherein the stiff thermoplastic composition has amelt volume flow rate of about 3.0 or less cm³/10 min at 230° C./2.16kg.
 18. The golf ball of claim 17, wherein the stiff thermoplasticcomposition has a melt volume flow rate of about 1.0 or less cm³/10 minat 230° C./2.16 kg.
 19. The golf ball of claim 15, wherein the stiffthermoplastic inner shell layer comprises two pre-molded half shells.20. The golf ball of claim 15, wherein the stiff thermoplastic innershell layer is blow molded, rotationally molded, or gas injectionmolded.